Hydrogel implants with varying degrees of crosslinking

ABSTRACT

The present disclosure relates to a hydrogel composition and methods of using the same. The hydrogel composition may include precursors that react with each other upon contact as well as precursors that react upon contact with an initiator. In embodiments, the resulting hydrogels may have varying levels of crosslinking with both denser and less dense regions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of, and priority to, U.S.Provisional Patent Application Ser. No. 61/348,896 filed on May 27,2010, the disclosure of which is hereby incorporated by reference in itsentirety.

BACKGROUND

Hydrogels may be used in the body for many different purposes. Forexample, hydrogels may be used as adhesives or sealants. Hydrogels mayalso be used in the formation of coatings or implants. Such implants orcoatings may also include drugs for local administration.

Hydrogels may be formed from precursor components. These components maybe reactive, i.e., the components react with one another upon contact,or they may be caused to react by exposure to external initiators, suchas ultraviolet (UV) light, ions, heat, visible light, gamma ray,electron beam, combinations thereof, and the like. Characteristics ofthe resulting hydrogel may be limited to the characteristics of theparticular type of precursor.

It would be advantageous to form a hydrogel that exhibits the propertiesof both reactive and initiated hydrogel precursors.

SUMMARY

The present disclosure provides hydrogels and methods for making andusing same. Devices including these hydrogels are also provided. Forexample, in embodiments, a hydrogel of the present disclosure may beutilized to attach a medical device to tissue.

In embodiments, a hydrogel composition of the present disclosure mayinclude a first reactive precursor including a multi-arm polyetherpossessing electrophilic groups, a second reactive precursor includingnucleophilic groups, and at least one initiated precursor including atleast one vinyl group.

Methods of the present disclosure may include, in embodiments,contacting a first reactive precursor with a second reactive precursorand an initiated precursor including at least one vinyl group;crosslinking the first reactive precursor and the second reactiveprecursor to form a first hydrogel; and exposing the initiated precursorto an initiator to initiate crosslinking of the initiated precursor.

In embodiments, crosslinking the initiated precursor may form a secondhydrogel. In embodiments, the first and second hydrogel may form aninterpenetrating network.

BRIEF DESCRIPTION OF DRAWINGS

Various embodiments of the present disclosure will be described hereinbelow with reference to the figures, in which:

FIG. 1A is a side view of a hydrogel implant in accordance with thepresent disclosure;

FIG. 1B is a cross-sectional view of the hydrogel of FIG. 1A depictingexposure to an initiator;

FIG. 1C is a cross-sectional view of the hydrogel of FIG. 1A followingexposure to an initiator;

FIG. 2A is a perspective view of a hydrogel implant in accordance withthe present disclosure;

FIG. 2B is a side view of the hydrogel of FIG. 2A depicting exposure toan initiator;

FIG. 2C is a cross-sectional view of the hydrogel of FIG. 2A followingexposure to an initiator;

FIG. 3A is a side view of a template used during formation of a hydrogelof the present disclosure;

FIG. 3B is an elevated view of a blocking device or screen for use witha template in accordance with the present disclosure;

FIG. 3C is a side view of a template and blocking device used inaccordance with the present disclosure;

FIG. 3D is a side view of a hydrogel implant of the present disclosure;

FIG. 4 is a graph depicting the modulus of a hydrogel implant of thepresent disclosure prior to and following cross-linking of an initiatedprecursor;

FIG. 5A is an elevated view of a mesh implant having a coating includingthe hydrogel of the present disclosure;

FIG. 5B is an elevated view of the implant of FIG. 5A followingdegradation of a portion of the hydrogel of the disclosure;

FIG. 6A is a cross-sectional view of a suture anchor formed using thehydrogel of the present disclosure;

FIG. 6B is a cross-sectional view of the suture anchor of FIG. 6Adepicting cross-linking of the initiated precursor;

FIG. 6C is a cross-sectional view of the suture anchor of FIG. 6A aftercross-linking of the initiated precursor;

FIG. 7A is an elevated view of an implant for adherence to tissue usingthe hydrogel of the present disclosure;

FIG. 7B is an elevated view of the implant of FIG. 7A prior tocross-linking of the initiated precursor;

FIG. 7C is an elevated view of the implant of FIG. 7A followingcross-linking of the initiated precursor;

FIG. 8 is a graph of the data presented in Table 2;

FIG. 9 is a graph comparing force applied and amount of compression foran initiated hydrogel and an uninitiated hydrogel;

FIG. 10 is a graph depicting the elastic modulus of different tissuesand other materials, including collagen and gelatin;

FIG. 11 is a depiction of a use of a composition of the presentdisclosure to repair a defect in tissue;

FIG. 12A is a view of an implant including a composition of the presentdisclosure, having a disperse region formed of one hydrogel within asecond hydrogel; and

FIG. 12B is an alternate view of an implant including a composition ofthe present disclosure, having disperse regions formed of one hydrogelwithin a second hydrogel.

DETAILED DESCRIPTION

Hydrogels are described herein that may be formed from crosslinkingreactive precursors, which do not require the use of an initiator, incombination with precursors that require external initiation, i.e.,initiated precursors. The precursor may be, e.g., a monomer or amacromer. As used herein the terms “hydrogel precursor(s)”, “firsthydrogel precursor”, and “second hydrogel precursor” may be used torefer to components that may be combined to form a hydrogel, either withor without the use of an initiator. Thus, these precursors may, inembodiments, include combinations of reactive precursors and initiatedprecursors. As used herein the terms “reactive precursor(s)”, “firstreactive hydrogel precursor(s)”, and “second reactive hydrogelprecursor(s)” include precursors that may crosslink upon exposure toeach other to form a hydrogel. As used herein the term “initiatedprecursor(s)”, “first initiated hydrogel precursor(s)” and “secondinitiated hydrogel precursor(s)” may be used to describe hydrogelprecursors that crosslink upon exposure to an external source, sometimesreferred to herein as an “initiator”. Initiators include, for example,ions, UV light, redox-reaction components, combinations thereof, as wellas other initiators within the purview of those skilled in the art.

The hydrogel precursors, whether reactive precursors or initiatedprecursors, may have biologically inert and water soluble cores. Whenthe core is a polymeric region that is water soluble, suitable polymersthat may be used include: polyethers, for example, polyalkylene oxidessuch as polyethylene glycol (“PEG”), polyethylene oxide (“PEO”),polyethylene oxide-co-polypropylene oxide (“PPO”), co-polyethylene oxideblock or random copolymers, and polyvinyl alcohol (“PVA”); poly(vinylpyrrolidinone) (“PVP”); poly(amino acids); poly (saccharides), such asdextran, chitosan, alginates, carboxymethylcellulose, oxidizedcellulose, hydroxyethylcellulose and/or hydroxymethylcellulose;hyaluronic acid; and proteins such as albumin, collagen, casein, andgelatin. In embodiments, combinations of the foregoing polymericmaterials may be utilized to form a core. The polyethers, and moreparticularly poly(oxyalkylenes) or poly(ethylene glycol) or polyethyleneglycol (“PEG”), may be utilized in some embodiments.

When the core is small in molecular nature, any of a variety ofhydrophilic functionalities may be used to make the hydrogel precursorswater soluble. In embodiments, functional groups like hydroxyl, amine,sulfonate and carboxylate, which are water soluble, may be used to makea precursor water soluble. For example, the N-hydroxysuccinimide (“NHS”)ester of subaric acid is insoluble in water, but by adding a sulfonategroup to the succinimide ring, the NHS ester of subaric acid may be madewater soluble, without affecting its ability to be used as a reactivegroup due to its reactivity towards amine groups.

In embodiments, a hydrogel may be formed from reactive precursorsthrough covalent, ionic, or hydrophobic bonds. Physical (non-covalent)crosslinks may result from complexation, hydrogen bonding, desolvation,Van der Waals interactions, ionic bonding, combinations thereof, and thelike, and may be initiated by mixing two precursors that are physicallyseparated until combined in situ or as a consequence of a prevalentcondition in the physiological environment, including temperature, pH,ionic strength, combinations thereof, and the like. Chemical (covalent)crosslinking may be accomplished by any of a number of mechanismsincluding, but not limited to, free radical polymerization, condensationpolymerization, anionic or cationic polymerization, step growthpolymerization, electrophile-nucleophile reactions, combinationsthereof, and the like.

In embodiments, the reactive precursor portion of the hydrogel may beformed from a single type of reactive precursor or multiple types ofreactive precursors. In other embodiments, where the hydrogel is formedfrom multiple types of reactive precursors, for example two reactiveprecursors, the reactive precursors may be referred to as a first andsecond reactive precursor. Where more than one reactive precursor isutilized, in embodiments, at least one of the reactive hydrogelprecursors may be a crosslinker, and at least one other reactivehydrogel precursor may be a macromolecule, and may be referred to hereinas a “functional polymer”.

In some embodiments, reactive precursors may include biocompatiblemulti-precursor systems that spontaneously crosslink when the precursorsare mixed, but wherein the two or more precursors are individuallystable for the duration of the deposition process. When the reactiveprecursors are mixed in an environment that permits reaction (e.g., asrelating to pH or solvent), the functional groups react with each otherto form covalent bonds. Reactive precursors become crosslinked when atleast some of the reactive precursors can react with more than one otherprecursor. For instance, a precursor with two functional groups of afirst type may be reacted with a crosslinking precursor that has atleast three functional groups of a second type capable of reacting withthe first type of functional groups.

Such reactive components include, for example, first reactive precursorspossessing electrophilic groups and second reactive precursorspossessing nucleophilic groups. Electrophiles react with nucleophiles toform covalent bonds. Covalent crosslinks or bonds refer to chemicalgroups formed by reaction of functional groups on different polymersthat serve to covalently bind the different polymers to each other. Incertain embodiments, a first set of electrophilic functional groups on afirst reactive precursor may react with a second set of nucleophilicfunctional groups on a second reactive precursor. In embodiments, suchsystems include a first reactive precursor including di- ormultifunctional alkylene oxide containing moieties, and a secondreactive precursor including macromers that are di- or multifunctionalamines.

In embodiments the reactive hydrogel precursors may be multifunctional,meaning that they may include two or more electrophilic or nucleophilicfunctional groups, such that, for example, an electrophilic functionalgroup on the first reactive hydrogel precursor may react with anucleophilic functional group on the second reactive hydrogel precursorto form a covalent bond. At least one of the first or second reactivehydrogel precursors includes more than two functional groups, so that,as a result of electrophilic-nucleophilic reactions, the precursorscombine to form crosslinked polymeric products.

In embodiments, each of the first and second reactive hydrogelprecursors include only one category of functional groups, either onlynucleophilic groups or only electrophilic functional groups, so long asboth nucleophilic and electrophilic reactive precursors are used in thecrosslinking reaction. Thus, for example, if the first reactive hydrogelprecursor has electrophilic functional groups such asN-hydroxysuccinimides, the second reactive hydrogel precursor may havenucleophilic functional groups such as amines. On the other hand, if thefirst reactive hydrogel precursor has electrophilic functional groupssuch as sulfosuccinimides, then the second reactive hydrogel precursormay have nucleophilic functional groups such as amines or thiols.

In embodiments, a multifunctional electrophilic polymer such as amulti-arm PEG functionalized with multiple NHS groups may be used as afirst reactive hydrogel precursor and a multifunctional nucleophilicpolymer such as trilysine may be used as a second reactive hydrogelprecursor. The multi-arm PEG functionalized with multiple NHS groupsmay, for example, have four, six or eight arms and a molecular weight offrom about 5,000 to about 25,000. Other examples of suitable first andsecond reactive hydrogel precursors are described in U.S. Pat. Nos.6,152,943; 6,165,201; 6,179,862; 6,514,534; 6,566,406; 6,605,294;6,673,093; 6,703,047; 6,818,018; 7,009,034; and 7,347,850, the entiredisclosures of each of which are incorporated by reference herein.

Certain properties of a hydrogel precursor may be useful, including, forexample, adhesion to a variety of tissues, desirable setting times toenable a surgeon to accurately and conveniently place the in situforming hydrogel precursors, high water content for biocompatibility,mechanical strength for use in sealants, and/or toughness to resistdestruction after placement. Synthetic materials that are readilysterilized and avoid the dangers of disease transmission that mayaccompany the use of natural materials may thus be used. Indeed, certainpolymerizable hydrogels made using synthetic precursors are within thepurview of those skilled in the art, e.g., as used in commerciallyavailable products such as FOCALSEAL® (Genzyme, Inc.), COSEAL®(Angiotech Pharmaceuticals), and DURASEAL® (Confluent Surgical, Inc).Other known hydrogels include, for example, those disclosed in U.S. Pat.Nos. 6,656,200; 5,874,500; 5,543,441; 5,514,379; 5,410,016; 5,162,430;5,324,775; 5,752,974; and 5,550,187.

The reaction conditions for forming crosslinked polymeric hydrogels fromreactive precursors may depend on the nature of the reactive precursorused. In embodiments, reactions are conducted in buffered aqueoussolutions at a pH of about 5 to about 12. Buffers include, for example,sodium borate buffer (pH 10) and triethanol amine buffer (pH 7). In someembodiments, organic solvents such as ethanol or isopropanol may beadded to improve the reaction speed or to adjust the viscosity of agiven formulation.

When the hydrogel precursors are synthetic (for example, when they arebased on polyalkylene oxide), it may be desirable to use molarequivalent quantities of the reactants. In some cases, molar excess of acrosslinker may be added to compensate for side reactions such asreactions due to hydrolysis of the functional group.

When choosing the reactive precursors, in embodiments a crosslinker andcrosslinkable polymer, at least one of the polymers may have more thantwo functional groups per molecule and, if it is desired that theresultant hydrogel be biodegradable, at least one degradable region. Inembodiments, each reactive polymer precursor may have more than twofunctional groups, and in embodiments, more than four functional groups.

The crosslinking density of the resultant biocompatible, crosslinkedpolymer formed from the reactive precursors may be controlled by theoverall molecular weight of the precursors, in embodiments a crosslinkerand functional polymer, and the number of functional groups availableper molecule. A lower molecular weight between crosslinks, such as 600Da, will give much higher crosslinking density as compared to a highermolecular weight, such as 10,000 Da. Elastic gels may be obtained withhigher molecular weight functional polymers with molecular weights ofmore than 3000 Da.

The crosslinking density may also be controlled by the overall percentsolids of the precursors, in embodiments crosslinker and functionalpolymer, in solutions. Increasing the percent solids increases thenumber of crosslinkable groups per unit volume and potentialcrosslinking density. Yet another method to control crosslink density isby adjusting the stoichiometry of nucleophilic groups to electrophilicgroups. A one to one ratio may lead to the highest crosslink density,however, other ratios of reactive functional groups (e.g.,electrophile:nucleophile) are envisioned to suit a desired formulation.

In embodiments, a first reactive precursor may be a multi-arm PEG andmay be functionalized by ring opening anhydrides containing a vinylgroup and end capped with NHS. The second reactive precursor may be amultifunctional amine component. The hydrogel of the disclosure may thusbe formed from at least two precursors.

In some embodiments, as noted above, hydrogel precursors may includeinitiated precursors. Initiated precursors for use in accordance withthe present disclosure may have a functional group that is ethylenicallyunsaturated. Such precursors possessing such ethylenically unsaturatedfunctional groups may have biologically inert and water soluble cores asdescribed above. Such cores may be functionalized by any means withinthe purview of those skilled in the art.

An ethylenically unsaturated functional group, in embodiments a vinylgroup, may be polymerized using an initiator to start the polymerizationreaction. Precursors with at least two ethylenically unsaturatedfunctional groups may form crosslinked polymers. Some compositions havecertain precursors with only one such functional group and additionalcrosslinked precursors with a plurality of functional groups forcrosslinking the precursors. Ethylenically unsaturated functional groupsmay be polymerized by various techniques, e.g., free radical,condensation, or addition polymerization. Exemplary initiated precursorsthat may be used in accordance with the present disclosure includeacrylates; anhydrides containing vinyl groups such as, for example,itaconic anhydride, maleic anhydride, citraconic anhydride, combinationsthereof, and the like. Other exemplary initiated precursors include, forexample, acrylic acid, methacrylic acid, phosphorylcholine containingmonomers, furanone functional vinyl monomers, potassium sulfopropylacrylate, potassium sulfopropyl methacrylate, n-vinyl pyrrolidone,hydroxyethyl methacrylate, vinyl monomers having a high refractiveindex, siloxane functional vinyl compounds, polyethylene glycol-siliconeco-monomers having vinyl groups, tris acrylate, pyrrole, liquidcrystalline vinyl monomers, liquid crystalline vinyl polymers,combinations thereof, and the like.

Suitable initiators utilized to polymerize initiated precursors include,but are not limited to, thermal initiators, photoactivatable initiators,oxidation-reduction (redox) systems, free radical initiators, radiation,thermal initiating systems, combinations thereof, and the like. Inembodiments, suitable sources of radiation include heat, visible light,ultraviolet (UV) light, gamma ray, electron beam, combinations thereof,and the like. In embodiments, photoinitiators may also be used. Suchphotoinitiators include, but are not limited to, free radicalinitiators, redox initiators such as ferrous-bromate, ammoniumpersulfate/acetic acid, ammonium persulfate-tetramethyl diamine,potassium persulfate/VA 044 (Wako Chemicals Inc., Richmond Va.), and thelike. UV light may also be used with dye mediated photooxidation,glutaraldehyde crosslinking, dexamethylene diisocyanate crosslinking,carbodiimide crosslinking, combinations thereof, and the like.

In embodiments, one or more hydrogel precursors having biodegradablelinkages present in between functional groups may be included to makethe hydrogel biodegradable or absorbable. In some embodiments, theselinkages may be, for example, esters, which may be hydrolyticallydegraded in physiological solution. The use of such linkages is incontrast to protein linkages that may be degraded by proteolytic action.A biodegradable linkage may also form part of a water soluble core ofone or more of the hydrogel precursors. Alternatively, or in addition,functional groups of hydrogel precursors may be chosen such that theproduct of the reaction between them results in a biodegradable linkage.For each approach, biodegradable linkages may be chosen such that theresulting biodegradable, biocompatible, crosslinked polymer degrades oris absorbed in a desired period of time. Generally, biodegradablelinkages may be selected that degrade the hydrogel under physiologicalconditions into non-toxic or low toxicity products.

Biodegradable crosslinkers or small molecules as described above may bereacted with proteins, such as albumin, other serum proteins, and/orserum concentrates, to generate crosslinked polymeric networks.Generally, aqueous solutions of crosslinkers may be mixed withconcentrated solutions of proteins to produce a crosslinked hydrogel.The reaction may be accelerated by adding a buffering agent, e.g., aborate buffer or triethanol amine, during the crosslinking step.

The crosslinking reaction leading to gelation may occur, in embodiments,within from about 1 second to about 5 minutes, in embodiments from about3 seconds to about 1 minute. Persons of ordinary skill in these artswill immediately appreciate that all ranges and values within theseexplicitly stated ranges are contemplated. In some cases gelation mayoccur in less than 10 seconds.

Degradation of a crosslinked hydrogel may depend upon the biodegradablesegment in the crosslinker as well as any enzymes to which the hydrogelis exposed. In the absence of any degrading enzymes, the crosslinkedpolymer may degrade solely by hydrolysis of the biodegradable segment.The rate of degradation may depend upon the polymer forming the watersoluble core and more specifically on the structure and location of anyester linkages formed. For example, an ester linkage may be formed in aring opening polymerization. The ring opening polymerization may occur,for example, between a PEG and a cyclic ester or an anhydride including,for example, furan-2,5-dione, 1,4-dioxane-2,5-dione, glutaric anhydride,succinic acid anhydride, maleic anhydride, itaconic anhydride, methylsuccinic anhydride, 2,2-dimethyl succinic anhydride, 2 dodecen-1-ylsuccinic anhydride, cis-1,2,3,6-tetrahydrophthalic anhydride, citraconicanhydride, 2,3-dimethyl maleic anhydride,1-cyclopentene-1,2-dicarboxylic anhydride, 3,4,5,6-tetrahydrophthalicanhydride, 3 ethyl-3-methyl glutaric anhydride, 3,3-dimethyl glutaricanhydride, 3-methyl glutaric anhydride, combinations thereof, and thelike. The resulting polymer may then be functionalized, in embodimentswith a succinimide group, and then may be utilized as a reactiveprecursor to form a hydrogel of the present disclosure (for example, bycombining with a crosslinker such as an amine). The monomer combinedwith PEG for the ring opening polymerization, and thus the resultingdegradable ester group, will influence the persistence of the hydrogelin vivo. The percent solids and arm length of monomers used to form thisreactive precursor may also influence its degradation rate.

For example, in embodiments, the product may be the ring openingpolymerization between PEG and a second component including an anhydridesuch as glutaric anhydride, itaconic anhydride, methyl succinicanhydride, 2,2-dimethyl succinic anhydride, 2 dodecen-1-yl succinicanhydride, cis-1,2,3,6-tetrahydrophthalic anhydride, citraconicanhydride, 2,3-dimethyl maleic anhydride,1-cyclopentene-1,2-dicarboxylic anhydride, 3,4,5,6-tetrahydrophthalicanhydride, 3 ethyl-3-methyl glutaric anhydride, 3,3-dimethyl glutaricanhydride, 3-methyl glutaric anhydride, combinations thereof, and thelike. The resulting product may form a hydrogel that degrades over aperiod of from about 6 weeks to about 8 weeks.

In other embodiments, the product of the ring opening polymerizationbetween PEG and succinic acid anhydride may degrade over a period offrom about 2 days to about 7 days. In embodiments where PEG and maleicanhydride are used, the product may degrade over a period of about sixmonths. The vinyl group in the ring opened maleic anhydride may beinvolved in a secondary vinyl polymerization. Thus, in embodiments, thevinyl group of the ring opened maleic anhydride may serve as aninitiated precursor.

The hydrophobicity generated by biodegradable blocks such asoligohydroxy acid blocks or the hydrophobicity of PPO blocks in PLURONICor TETRONIC polymers may be helpful in dissolving small organic drugmolecules. Other properties which will be affected by incorporation ofbiodegradable or hydrophobic blocks include: water absorption;mechanical properties; and thermosensitivity.

Synthetic crosslinked gels degrade due to hydrolysis of thebiodegradable region. The degradation of gels containing syntheticpeptide sequences may depend on the specific enzyme necessary fordegradation of the sequence and its concentration. In some cases, aspecific enzyme may be added during the crosslinking reaction toaccelerate the degradation process.

The hydrogel precursors may be placed into solution prior to use, withthe solution being delivered to tissue. Where two solutions areemployed, each solution may contain one or more precursors that mayreact with one another upon contact. The solutions may be separatelystored and mixed when delivered to tissue.

Any solutions utilized as part of an in situ forming material systemshould not contain harmful or toxic solvents. In embodiments, theprecursor(s) may be substantially soluble in a solvent such as water toallow application in a physiologically-compatible solution, such asbuffered isotonic saline. Water-soluble coatings may form thin films,but in embodiments may also form three-dimensional gels of controlledthickness. The gel may also be biodegradable, so that it does not haveto be retrieved from the body. The term “biodegradable” as used hereinis defined to include both bioabsorbable and bioresorbable materials. Bybiodegradable, it is meant that the materials decompose, or losestructural integrity under body conditions (e.g., enzymatic degradationor hydrolysis) or are broken down (physically or chemically) underphysiologic conditions in the body such that the degradation productsare excretable or absorbable by the body.

Various applications may require different characteristics of thehydrogel. Generally, the hydrogel precursors should be selected on thebasis of exhibited biocompatibility and lack of toxicity.

In embodiments, a hydrogel may be formed from at least one reactiveprecursor (capable of crosslinking, for example, by free radicalpolymerization), and at least one initiated precursor, or made withthree or more precursors, with one or more of the precursorsparticipating in crosslinking to form the in situ forming material.

Prior to hydrogel formation, the initiated precursor, in embodiments alinear PEG acrylate, may be reconstituted in a high pH buffer, forexample sodium borate, having a pH from about 7 to about 11, inembodiments from about 8 to about 10. The initiated precursor, inembodiments a multi-arm PEG having electrophilic functional groups, maybe reconstituted with a low pH buffer, such as, sodium phosphate, havinga pH from about 3 to about 6, in embodiments from about 4 to about 5.

In embodiments, a linear PEG acrylate may be used as the initiatedprecursor. In embodiments, a hydrogel may thus be formed by contacting afirst reactive hydrogel precursor, a second reactive hydrogel precursor,and the initiated precursor. The hydrogel may form upon reaction of thefirst reactive precursor and the second reactive precursor. Thecomponents may also be exposed to an initiator to crosslink theinitiated precursor thereby creating a denser hydrogel.

In embodiments, the resulting hydrogel may form an interpenetratingnetwork. In embodiments, an interpenetrating network may be formed fromtwo hydrogel networks, i.e., a hydrogel formed by at least two reactiveprecursors in combination with an initiated precursor. In otherembodiments, the interpenetrating network could be formed from aninitiated precursor that also possesses reactive groups. Such aprecursor can both react with another reactive precursor and beinitiated upon exposure to an initiator.

For example, in embodiments, a first hydrogel may form between amulti-arm PEG and trilysine. A second hydrogel may be formed by exposingan ethylenically unsaturated monomer to an initiator. These twohydrogels may be combined prior to exposure to the initiator. Exposureof these hydrogels, to the initiator results in an interpenetratingnetwork of hydrogels, each of which may have separate properties such asvarying degradation rates. Additionally, varying the amount of reactiveprecursors and initiated precursors may result in different propertiesof the resulting composition.

In other embodiments, a multi-arm PEG may be functionalized with vinylgroups and reacted with trilysine to form a first hydrogel. Byinitiating the PEG functionalized with vinyl groups with an initiator,the crosslinking of the hydrogel may be increased due to thecrosslinking of the vinyl groups, thereby forming an interpenetratingnetwork. In other embodiments, a multi-arm PEG functionalized with vinylgroups may react to a limited extent with amines, followed by theaddition of an initiator to increase crosslinking of the vinyl groups.

Where the reactive precursors from a first hydrogel, the initiatedprecursor forms a second hydrogel, and the two hydrogels together forman interpenetrating network, in embodiments the first hydrogel formedfrom the reactive precursors may degrade more quickly than the secondhydrogel formed from the initiated precursor, thereby forming spacespermitting healing by means of, for example, tissue in-growth,vascularization, combinations thereof, and the like.

In embodiments, the hydrogel of the present disclosure, having aninterpretation network with varying degrees of degradation, may act as atissue scaffold, thereby providing a means for tissueintegration/ingrowth. Tissue scaffolds also are capable of providingcells with growth and development components. Thus, where the hydrogelof the present disclosure is utilized as a tissue scaffold, it mayassist in native tissue regrowth by providing the surrounding tissuewith needed nutrients and bioactive agents. In some embodiments, asdiscussed herein, the hydrogel itself may include a natural component,such as collagen, gelatin, hyaluronic acid, combinations thereof, andthe like, and thus the natural component may be released or otherwisedegrade at the site of implantation as the tissue scaffold degrades.

In other embodiments, a hydrogel composition of the present disclosuremay possess two hydrogels, with one dispersed within the other. Forexample, in embodiments, a composition of the present disclosure mayinclude the first hydrogel formed from reactive precursors, with atleast one disperse region within the first hydrogel, the disperse regionformed of a second hydrogel formed from an initiated precursor. In otherembodiments, a first hydrogel formed of reactive precursors may form atleast one disperse region within a second hydrogel formed from aninitiated precursor. The disperse region formed by one hydrogel may formone region, e.g., a central region or core, within a second hydrogel, orthe disperse region formed by one hydrogel may form many small regionswithin a second hydrogel.

Varying the concentrations of the reactive and initiated precursors mayresult in differing properties of the resulting hydrogel. For example,in embodiments, a solution may contain an acrylate having a molecularweight from about 200 g/mole to about 50,000 g/mole, in embodiments fromabout 500 g/mole to about 35,000 g/mole, at a concentration of fromabout 5 g/ml to about 40 g/ml, in embodiments about 10 g/ml to about 20g/ml. The solution may also contain a photoinitiator at a concentrationof from about 5 mg/ml to about 100 mg/ml, in embodiments from about 10mg/ml to about 20 mg/ml. The photoinitiator may be, for example,4,4′-Bis(diethyl amino) benzophenone, 2,2-dimethoxy-2-phenylacetophenone, camphorquinone/4-dimethyl amino benzoic acid, eosin,azobisisobutyronitrile (AIBN), dimethoxy benzophenone, combinationsthereof, and the like. The acrylate/photoinitiator solution may have aconcentration from about 4.25% to about 17%, in embodiments from about6% to about 14%, in embodiments about 8.5%. In embodiments theacrylate/photoinitiator solution may be combined with a multi-arm PEGmay be in a sodium phosphate buffer at a concentration of from about0.05 g/ml to about 2 g/ml, in embodiments about 0.1 g/ml to about 1g/ml, in embodiments about 0.26 g/ml. These solutions may react to forma hydrogel of the present disclosure.

As stated above, addition of the initiated precursor to the reactiveprecursors and subsequent exposure to an initiator may alter propertiesof the resulting hydrogel. Additionally, the ratio of initiatedprecursor to reactive precursors may influence mechanical properties. Asdepicted graphically in FIG. 4 and listed in Table 1 below, thepercentage of initiated precursor present in the mixture of reactive andinitiated precursors greatly impacts the strength of the hydrogelfollowing cross-linking of the reactive hydrogels.

TABLE 1 10% initiated 20% initiated 10% initiated 20% initiated(uncross- (uncross- (cross- (cross- linked): linked): linked): linked):Hydrogel 90% reactive 80% reactive 90% reactive 80% reactive Modulus(KPa) ~80 Kpa ~40 KPa ~100 KPa ~720 KPa

Thus, in accordance with the present disclosure, a hydrogel may beformed by two different mechanisms: the reaction of the reactiveprecursors; and the initiation of the initiated precursors. Theresulting hydrogel may, in turn, thus be made of two differenthydrogels. For example, a first hydrogel may be formed from the reactiveprecursors, while a second hydrogel may be formed from the initiatedprecursors.

The first hydrogel may include the first reactive precursor in an amountfrom about 10% to about 30%, in embodiments from about 15% to about 25%,and the second reactive precursor in an amount from about 70% to about90%, in embodiments from about 75% to about 85%. In other embodiments,the first hydrogel may include the first reactive precursor in an amountfrom about 70% to about 90%, in embodiments from about 75% to about 85%,and the second reactive precursor in an amount from about 10% to about30%, in embodiments from about 15% to about 25%.

The modulus of the materials utilized to form a composition of thepresent disclosure may depend upon the end use of the composition. Forexample, a composition applied to tissue for use as a tissue scaffoldmay have a much lower modulus than a composition intended for use toattach a medical device to tissue.

In embodiments, the first hydrogel formed from the reactive precursorsmay have a modulus from about 5 kilopascal (kPa) to about 90 kPa, inembodiments from about 10 kPa to about 50 kPa, and the second hydrogelformed from the initiated precursor may have a modulus from about 50 kPato about 5,000 kPa, in embodiments from about 100 kPa to about 4,000kPa.

Depending on the degradation rates of the resulting hydrogels, theportion of the hydrogel formed by the reactive precursors may degrademore quickly than the portion of the hydrogel formed by the initiatedprecursor, thereby forming spaces in the hydrogel which may permittissue in-growth, visualization, and the like. In embodiments, the firsthydrogel formed from reactive precursors may degrade over a period oftime from about 1 week to about 12 weeks, in embodiments from about 4weeks to about 10 weeks, while the second hydrogel formed from initiatedprecursors may degrade over a period of at least about 2 weeks, inembodiments it may not degrade, i.e., it remains permanently in thebody. In some embodiments the second hydrogel may degrade over a periodof at least about 6 months. In some embodiments, the second hydrogel maydegrade over a period from about 6 weeks to about 6 months.

Where the second hydrogel forms a barrier layer over the first hydrogel,the first hydrogel may have a modulus from about 5 kPa to about 60 kPa,in embodiments from about 10 kPa to about 50 kPa, and the secondhydrogel forming the barrier layer may have a modulus from about 100 kPato about 1,000 kPa, in embodiments from about 200 kPa to about 900 kPa.The first hydrogel may thus degrade over a period from about 1 day toabout 7 days, in embodiments from about 2 days to about 6 days, and thebarrier layer may degrade over a period of at least about 6 months, inembodiments from about 6 months to about 12 months.

Where the hydrogels form an interpenetrating network, the first hydrogelmay have a modulus from about 5 kPa to about 20 kPa, in embodiments fromabout 8 kPa to about 17 kPa, and the second hydrogel may have a modulusfrom about 50 kPa to about 500 kPa, in embodiments from about 75 kPa toabout 400 kPa.

Where the hydrogel is used to form an attachment device for attaching amedical device to tissue, the first precursor may have a modulus fromabout 10 kPa to about 50 kPa, in embodiments from about 15 kPa to about45 kPa, and the second hydrogel may have a modulus from about 60 kPa toabout 200 kPa, in embodiments from about 75 kPa to about 175 kPa. Theinitiated precursor forming the second hydrogel may be present in anamount from about 40% to about 90% by weight of the attachment device,in embodiments from about 50% to about 75% by weight of the attachmentdevices. The first hydrogel may degrade over a period from about 1 dayto about 7 days, in embodiments from about 2 days to about 6 days, andthe second hydrogel may degrade over a period of at least about 6months, in embodiments from about 6 months to about 12 months.

Where the composition of the present disclosure is used to deliver abioactive agent, the first hydrogel may have a modulus from about 5 kPato about 50 kPa, in embodiments from about 10 kPa to about 40 kPa, andthe second hydrogel may have a modulus from about 10 kPa to about 100kPa, in embodiments from about 20 kPa to about 80 kPa.

In embodiments, one reactive precursor and one initiated precursor maybe placed in a first solution, and a second reactive precursor with anoptional initiated precursor may be placed in a second solution. Uponthe mixture of these solutions, the reactive precursors may crosslink toform a base hydrogel, while the initiated precursors may not crosslinkuntil exposed to an initiator. In other embodiments, one reactiveprecursor and one or more initiated precursor(s) may be placed in afirst solution, and a second reactive precursor may be placed in asecond solution.

The density of a hydrogel resulting from a combination of reactiveprecursors and initiated precursors may be further controlled based onthe initiator used to form the hydrogel. For example, a multi-arm PEGcapped with NHS first reactive hydrogel precursor, a multifunctionalamine second reactive hydrogel precursor, and a linear PEG acrylateinitiated precursor, may result in a hydrogel containing unreactedacrylate groups. Upon exposure to an initiator, in embodiments UV light,the acrylate groups may react with themselves as well as the terminalends of the PEG arms. By controlling exposure to the initiator, theamount of acrylate crosslinking may thus be used to further adjust thedensity of the hydrogel.

Adjustment of the density of the hydrogel may affect the permeability ofthe resulting hydrogel, e.g., a denser hydrogel may be less permeable.In embodiments, the initiated precursor(s) may be densely crosslinked,thereby forming a less permeable barrier layer within or on the exteriorof the hydrogel formed from the reactive precursors, thus forming acomposite hydrogel composition.

In accordance with the present disclosure, the polymer formed from aninitiated precursor may account for from about 5 percent by weight toabout 30 percent by weight of the resulting composite hydrogel, inembodiments from about 10 percent by weight to about 20 percent byweight of the resulting hydrogel, with the polymer formed from thereactive precursors accounting for from about 5 percent by weight toabout 60 percent by weight of the resulting hydrogel, in embodimentsfrom about 15 percent by weight to about 40 percent by weight of theresulting hydrogel. The remainder of the resulting hydrogel will be madeup of fluid/water.

Formation of a hydrogel of the present disclosure may take place insitu. In other embodiments, the hydrogel formation may take place exvivo, that is, prior to placement in situ. The combination of reactiveprecursors with initiated precursors may allow for the formation ofhydrogels that exhibit properties of both types of crosslinkedprecursors. In some embodiments, the hydrogel may be molded into adesired shape within a tissue defect prior to exposing a surface of thehydrogel to an initiator.

In situ formation, in general, may be accomplished by having a hydrogelprecursor that may be activated at the time of application to tissue toform a crosslinked hydrogel. Activation may be made before, during, orafter application of the precursor to tissue. Activation includes, forinstance, triggering a polymerization process, initiating a free radicalpolymerization, or mixing precursors with functional groups that reactwith each other. Thus, in situ polymerization includes activation ofchemical moieties to form covalent bonds and to create an insolublematerial, e.g., a hydrogel, at a location where the material is to beplaced on, within, or both on and within, a patient. In situpolymerizable polymers may be prepared from hydrogel precursors that maybe reacted such that they form a polymer within the patient. As notedabove, in embodiments, a hydrogel may be formed from both reactiveprecursors and initiated precursors.

As stated above, the hydrogel precursors may be placed into solutionprior to use, with the solution being delivered to the patient. Inembodiments, the precursors may be substantially soluble in water toallow application in a physiologically-compatible solution, such asbuffered isotonic saline. One may use a dual syringe or similar deviceto apply the precursor solutions, such as those described in U.S. Pat.Nos. 4,874,368; 4,631,055; 4,735,616; 4,359,049; 4,978,336; 5,116,315;4,902,281; 4,932,942; 6,179,862; 6,673,093; 6,152,943; and 7,347,850.

Generally, two or more hydrogel precursors may be applied via a sprayerto the tissue to form a coating in situ. For example, two reactiveprecursor solutions, at least one of which containing an initiatedprecursor, may be placed in separate chambers of the sprayer. When thesprayer is activated, the emergent spray contacts tissue, resulting inmixing and crosslinking of the two reactive precursors to form a coating(for example a hydrogel) on the tissue surface.

In embodiments, the sprayer includes separate spray nozzles for each oftwo or more reactive precursor solutions, with each nozzle surrounded bya separate or common gas flow outlet. The reactive precursor solutionsare stored in separate compartments, e.g., a multi-cylinder syringe, andtransferred under pressure to the spray nozzles. In the presence of gasflow through the gas flow outlets, the crosslinkable solutions areatomized and mixed in the gas flow to form a spray, which may be used tocoat tissue. In certain embodiments, a CO₂ gas cartridge may bereversibly or permanently mounted on the device to facilitate deliveryof the precursors.

Certain embodiments include combining a suction-irrigation apparatuswith a hydrogel precursor delivery device. An advantage of such acombination is that the tissue may be cleansed of clotted blood andadhesioniogenic materials and the combination may allow for placement ofa hydrogel using a single device.

The hydrogel of the present disclosure may also be used to form, forexample, components such as adhesives, hemostats, sealants, implants,protective barriers, drug delivery devices, combinations thereof, andthe like. Implants which may be formed include, for example, matrices,artificial blood vessels, heart valves, artificial organs, boneprostheses, implantable lenticules, vascular grafts, stents, sutures,staples, clips, meshes, slings, screws, pins, cables, cartilageimplants, spinal implants, and combinations thereof. The implant mayalso be used to augment of soft or hard tissue within the body of amammal. Examples of soft tissue augmentation applications include:sphincter (e.g., urinary, anal, esophageal) augmentation; use asartificial skin; the treatment of rhytids; and/or the treatment ofscars. Examples of hard tissue augmentation include the repair and/orreplacement of bone and/or cartilaginous tissue. Other tissue defectswhich may be treated with a hydrogel and/or implant of the presentdisclosure include, for example, sphincters, including lower esophagealsphincter bulking to treat gastroesophageal reflux disease (GERD);periurethral bulking to treat urinary incontinence; creating cushionsbetween tissue layers to assist in tissue dissections and/or resections,for example in polypectomy procedures; preventing adhesions; plasticsurgery as a dermal filler; treatment of defects in lips, breasts, andother body tissues; combinations thereof, and the like.

In embodiments, the hydrogel may be used to form a semi-flexiblevertebral disc having a rigid or dense exterior formed by the hydrogelproduced by the initiated precursor and a less dense, more flexible,interior formed by the hydrogel produced by the reactive precursors. Inembodiments, a template may be used that is shaped to resemble thevertebral disc needing replacement. The template may be filled with thehydrogel precursors to form the hydrogel. The hydrogel may then beexposed to an initiator so as to induce crosslinking of the initiatedprecursor on the surface, thereby forming a dense outer or barrier layerencompassing the hydrogel interior.

For formation of a vertebral disc implant, the implant may be formedduring surgery, or prior to surgery. For example, the appropriateimplant size may be determined during surgery by first using a caliperor similar device to measure the length and dimensions of the defect tobe repaired. The surgical staff may then utilize a template as describedabove to form an implant of the desired size by introducing the reactiveprecursors and initiated precursor into the template and allowing thereactive precursors to form the first hydrogel. The composition may thenbe subjected to the initiator, thereby forming the dense outer orbarrier layer encompassing the first hydrogel interior, therebyproducing the vertebral disc implant.

Alternatively, using radiographic techniques, including X-ray, MRI, andthe like, the appropriate implant size may be determinedpre-operatively, with the vertebral disc implant formed as describedabove prior to surgery.

In other embodiments, the reactive precursors may be applied to a defectin tissue, thereby forming a first hydrogel therein, with the initiatedprecursor forming a second hydrogel, which functions as a barrier layer,on at least a portion of a surface of the first hydrogel covering thedefect in tissue.

The selection of materials for forming the hydrogels may be tailoreddepending upon the end use of the hydrogel composition of the presentdisclosure. For example, polyethylene glycol-based polymers may bedesirable where protein adhesion is to be prevented; hyaluronicacid-based polymers may be desirable where enhanced sliding, gliding,and/or lubricity is desired; collagen-based polymers may be desirable toprovide adhesion sites for cellular attachment; synthetic polymers maybe desirable for long-term and/or permanent implants; and the like.

In embodiments, reactive hydrogel precursors may form a hydrogelcontaining a bioactive agent. An initiated precursor may be added to theprecursors prior to or following reaction. The initiated precursor maythen be initiated forming a barrier layer. The barrier layer may inhibitdiffusion of the bioactive agent from the hydrogel formed by thereactive precursors in the direction of the barrier, thereby forcingunidirectional administration of the bioactive agent, i.e., in adirection opposite the barrier layer.

In embodiments, reactive and initiated hydrogel precursors may also becombined in a layer on the bottom of a mold. The base layer may then beexposed to an initiator to further cross-link the bottom layer. A secondlayer including the precursors may then be placed on the bottom layerand a screen may be used to limit the exposure of the second layer tothe initiator. Thus, the un-screened portion may further crosslink,while the screened portion does not crosslink, thereby providing varyingdegrees of cross-linking in the layer. Additional layers may be addedusing the same or different screens. Each layer may contain a bioactiveagent which may be the same or different. The varied amount ofcrosslinking may provide alternate rates of degradation, therebyproviding varying release rates of the bioactive agent. The initiatormay be contacted with the hydrogel before or after contact with themedical device. Medical devices which may be attached to tissue with thehydrogel include sutures, staples, tacks, clips, rivets, combinationsthereof, and the like.

In other embodiments, a mixture of reactive and initiated hydrogelprecursors may be sprayed or applied to an implant such as a mesh. Themesh may be a filamentous substrate including an initiator for theinitiated hydrogel. The reactive hydrogel may form a coating over themesh. The coating may degrade over several days, thereby preventingadhesions. The degradation of the coating may also serve to create poresin the mesh for tissue in-growth. The initiated hydrogel may not undergothe same degradation, thereby maintaining adherence of the mesh totissue.

In other embodiments, a mesh may be contacted with reactive precursorsand initiated precursor(s), the reactive precursors may form a firsthydrogel, and the initiated precursor may form a second hydrogel tosecure the mesh to tissue. In embodiments, the first hydrogel may formprior to the second hydrogel. In other embodiments the second hydrogelmay be formed prior to the first hydrogel. In some embodiments, wherethe first hydrogel forms prior to the second hydrogel, the firsthydrogel may allow for the temporary adherence and placement of the meshto tissue, permitting repositioning and re-adherence of the mesh totissue, after which the second hydrogel is formed for permanentplacement of the mesh. In such a case, the first hydrogel should remaintacky for adherence and re-adherence of the mesh to tissue for at least10 minutes, in embodiments from about 10 minutes to about 40 minutes, inembodiments from about 12 minutes to about 25 minutes. After this time,the second hydrogel may be formed.

In embodiments, a mesh implant of the present disclosure may include afilamentous substrate possessing a film coating on at least a portion ofthe filamentous substrate. In embodiments, the film coating may includea freeze-dried composition including an initiated precursor having atleast one vinyl group, in combination with a first hydrogel including afirst reactive precursor including a multi-arm polyether possessingelectrophilic groups, and a second reactive precursor includingnucleophilic groups. In use, the first hydrogel can be re-hydrated toreleasably attach the mesh to tissue, and the initiated precursor can beexposed to an initiator to form a second hydrogel securely affixing themesh to tissue. The first hydrogel may be re-hydrated upon contact withbody fluids, the addition of saline, combinations thereof, and the like.

In yet other embodiments, a mixture of reactive and initiated hydrogelprecursors may be combined and injected below the surface of tissue andalso allowed to pool on the tissue surface. The hydrogel thus formed,both underneath and on the tissue surface, may be contacted with asuture or other medical device. The medical device may then be contactedwith the hydrogel anchor, which helps affix the device to tissue. Forexample, for a suture anchor, the hydrogel may be formed and a suturethreaded therethrough. The reactive precursors may form a first hydrogelprior to formation of a second hydrogel from the initiated precursors.In other embodiments, the hydrogel formed from the initiated precursorsmay be formed prior to the hydrogel formed from the reactive precursors.

In other embodiments, a mixture of reactive and initiated hydrogelprecursors may be used to form an implant attachment device such as ananchor or rivet. A mesh or other implant may be secured to tissue by theprecursors. The implant may have holes through which the mixture isextruded, similar to the suture anchor described above, i.e., thehydrogel could be injected below the surface of tissue and allowed topool on the surface of an implant covering the tissue. The reactivehydrogel may then be formed to hold the implant in place and, followingimplantation, the hydrogel mixture may be exposed to an initiatorsecuring the implant to the tissue.

For example, in embodiments, a mixture may be formed including a firstreactive precursor having a multi-arm polyether possessing electrophilicgroups, a second reactive precursor having nucleophilic groups, and atleast one initiated precursor having at least one vinyl group. A meshmay be contacted with tissue, and the mixture may be injected throughthe mesh into the tissue. The mixture may form a first hydrogel bothunderneath and on the tissue surface, in contact with the mesh. Theinitiated precursor may be contacted with an initiator to form a secondhydrogel, thereby forming an attachment device for attaching the mesh tothe tissue.

The hydrogel precursor(s) and/or the resulting hydrogel may containvisualization agents to improve their visibility during surgicalprocedures. Visualization agents may be selected from a variety ofnon-toxic colored substances, such as dyes, suitable for use inimplantable medical devices. Suitable dyes are within the purview ofthose skilled in the art and may include, for example, a dye forvisualizing a thickness of the hydrogel as it is formed in situ, e.g.,as described in U.S. Pat. No. 7,009,034. In some embodiments, a suitabledye may include, for example, FD&C Blue #1, FD&C Blue #2, FD&C Blue #3,FD&C Blue #6, D&C Green #6, methylene blue, indocyanine green, othercolored dyes, and combinations thereof. It is envisioned that additionalvisualization agents may be used such as fluorescent compounds (e.g.,flurescein or eosin), x-ray contrast agents (e.g., iodinated compounds),ultrasonic contrast agents, and MRI contrast agents (e.g., Gadoliniumcontaining compounds).

The visualization agent may be present in a hydrogel precursor solution.The colored substance may or may not become incorporated into theresulting hydrogel.

The visualization agent may be used in small quantities, in embodimentsless than 1% weight/volume; in embodiments less that 0.01%weight/volume; and in embodiments less than 0.001% weight/volumeconcentration.

Hydrogel precursors, as well as their reaction products, may also beused for drug therapy or delivery of bioactive agents. In embodiments,the hydrogel may be coated with or include additional bioactive agents.The term “bioactive agent”, as used herein, is used in its broadestsense and includes any substance or mixture of substances that haveclinical use. Consequently, bioactive agents may or may not havepharmacological activity per se, e.g., a dye. Alternatively a bioactiveagent could be any agent, which provides a therapeutic or prophylacticeffect, a compound that affects or participates in tissue growth, cellgrowth, cell differentiation, an anti-adhesive compound, a compound thatmay be able to invoke a biological action such as an immune response, orcould play any other role in one or more biological processes. It isenvisioned that the bioactive agent may be applied to the hydrogel inany suitable form of matter, e.g., films, powders, liquids, gels and thelike.

As noted above, in embodiments that include a multi-arm PEG or PEG star,the bioactive agent may be incorporated into the core of the PEG, thearms of the PEG, or combinations thereof. In embodiments, the bioactiveagent may be attached to a reactive group in the PEG chain. Thebioactive agent may be bound covalently, non-covalently, i.e.,electrostatically, through a thiol-mediated or peptide-mediated bond, orusing biotin-adivin chemistries and the like.

Examples of classes of bioactive agents which may be utilized inaccordance with the present disclosure, include, for exampleanti-adhesives; antimicrobials; analgesics; antipyretics; anesthetics;antiepileptics; antihistamines; anti-inflammatories; cardiovasculardrugs; diagnostic agents; sympathomimetics; cholinomimetics;antimuscarinics; antispasmodics; hormones; growth factors; musclerelaxants; adrenergic neuron blockers; antineoplastics; immunogenicagents; immunosuppressants; gastrointestinal drugs; diuretics; steroids;lipids; lipopolysaccharides; polysaccharides; platelet activating drugs;clotting factors; and enzymes. It is also intended that combinations ofbioactive agents may be used.

Anti-adhesive agents can be used to prevent adhesions from formingbetween the hydrogel, in embodiments a hydrogel implant, and surroundingtissues. Some examples of these agents include, but are not limited tohydrophilic polymers such as poly(vinyl pyrrolidone), carboxymethylcellulose, hyaluronic acid, polyethylene oxide, poly vinyl alcohols, andcombinations thereof.

Suitable antimicrobial agents, which may be included as a bioactiveagent include: triclosan, also known as2,4,4′-trichloro-2′-hydroxydiphenyl ether; chlorhexidine and its salts,including chlorhexidine acetate, chlorhexidine gluconate, chlorhexidinehydrochloride, and chlorhexidine sulfate; silver and its salts,including silver acetate, silver benzoate, silver carbonate, silvercitrate, silver iodate, silver iodide, silver lactate, silver laurate,silver nitrate, silver oxide, silver palmitate, silver protein, andsilver sulfadiazine; polymyxin; tetracycline; aminoglycosides, such astobramycin and gentamicin, rifampicin, bacitracin, neomycin,chloramphenicol, and miconazole; quinolones such as oxolinic acid,norfloxacin, nalidixic acid, pefloxacin, enoxacin and ciprofloxacin;penicillins such as oxacillin and pipracil; nonoxynol 9; fusidic acid;cephalosporins; and combinations thereof. In addition, antimicrobialproteins and peptides such as bovine lactoferrin and lactoferricin B maybe included as a bioactive agent.

Other bioactive agents, which may be included as a bioactive agentinclude: local anesthetics; non-steroidal antifertility agents;parasympathomimetic agents; psychotherapeutic agents; tranquilizers;decongestants; sedative hypnotics; steroids; sulfonamides;sympathomimetic agents; vaccines; vitamins; antimalarials; anti-migraineagents; anti-parkinson agents such as L-dopa; anti-spasmodics;anticholinergic agents (e.g., oxybutynin); antitussives;bronchodilators; cardiovascular agents, such as coronary vasodilatorsand nitroglycerin; alkaloids; analgesics; narcotics such as codeine,dihydrocodeinone, meperidine, morphine and the like; non-narcotics, suchas salicylates, aspirin, acetaminophen, d-propoxyphene and the like;opioid receptor antagonists, such as naltrexone and naloxone;anti-cancer agents; anti-convulsants; anti-emetics; antihistamines;anti-inflammatory agents, such as hormonal agents, hydrocortisone,prednisolone, prednisone, non-hormonal agents, allopurinol,indomethacin, phenylbutazone and the like; prostaglandins; cytotoxicdrugs; chemotherapeutics, estrogens; antibacterials; antibiotics;anti-fungals; anti-virals; anticoagulants; anticonvulsants;antidepressants; antihistamines; and immunological agents.

Other examples of suitable bioactive agents which may be included in thehydrogel include, for example, viruses and cells; peptides, polypeptidesand proteins, as well as analogs, muteins, and active fragments thereof;immunoglobulins; antibodies; cytokines (e.g., lymphokines, monokines,chemokines); blood clotting factors; hemopoietic factors; interleukins(IL-2, IL-3, IL-4, IL-6); interferons (β-IFN, α-IFN and γ-IFN);erythropoietin; nucleases; tumor necrosis factor; colony stimulatingfactors (e.g., GCSF, GM-CSF, MCSF); insulin; anti-tumor agents and tumorsuppressors; blood proteins such as fibrin, thrombin, fibrinogen,synthetic thrombin, synthetic fibrin, synthetic fibrinogen;gonadotropins (e.g., FSH, LH, CG, etc.); hormones and hormone analogs(e.g., growth hormone); vaccines (e.g., tumoral, bacterial and viralantigens); somatostatin; antigens; blood coagulation factors; growthfactors (e.g., nerve growth factor, insulin-like growth factor); bonemorphogenic proteins; TGF-B; protein inhibitors; protein antagonists;protein agonists; nucleic acids, such as antisense molecules, DNA, RNA,RNAi; oligonucleotides; polynucleotides; and ribozymes.

The bioactive agent may be released from the hydrogel as a bolus, over aperiod of time, or combinations thereof. The reactive precursors mayform a hydrogel that is more permeable, allowing diffusion of abioactive agent from the hydrogel. In embodiments, the initiatedprecursor may be crosslinked to form a barrier layer over the hydrogelformed from the reactive precursors, thereby, reducing diffusion of abioactive agent therefrom.

Embodiments of the present disclosure will now be described withreference to the figures. With reference to FIG. 1A, reactive precursorscrosslink to form a hydrogel 100, optionally containing a bioactiveagent 110 on tissue 120 in situ. As shown in FIG. 1B, the hydrogel 100may then be exposed to an initiator 130 such as UV light to initiatereaction of initiated precursor(s) included therein. FIG. 1C showsformation of a barrier layer 140 on hydrogel 100, which is formed by theinitiated precursor(s) and inhibits diffusion of the bioactive agent 110from the hydrogel. Thus, the bioactive agent 110 may diffuseunidirectionally into the tissue 120 in need of the bioactive agent 110,but not diffuse into any lumen or area adjacent tissue 120 due to thepresence of barrier layer 140. Unidirectional distribution of abioactive agent may be used, for example, for direct delivery ofchemotherapeutic agents to dura, lung, or bowel; anti-clotting drugs tocardiovascular tissues; anti-arrhythmia drugs to the heart;anti-inflammatories or analgesics to wounded tissues; hemostats to treatwounded tissue; and the like, and combinations of these.

As shown in FIG. 2A, a hydrogel 200 may be formed from reactiveprecursors in the shape of a spinal disc. FIG. 2B is a side view of thehydrogel 200, which may be exposed to an initiator 220 to gel anyinitiated precursors within hydrogel 200. FIG. 2C is a cross-sectionalview of the resulting disc having a hydrogel 200 formed from reactiveprecursors and a denser barrier layer 230 formed from initiatedprecursors. The reaction of the initiated precursors may increase thedensity of the surface area, thereby creating a “skin” or barrier ofdenser hydrogel 230 on the surface of hydrogel 200. In such a manner, animplant such as a non-degradable vertebral disc replacement may beformed.

In embodiments, a two-phase hydrogel implant may be formed. For example,the two-phase hydrogel implant may be formed using a template and/or ascreen. The template and screen(s) may be any shape or size. Inembodiments, the template may be a cylinder having a base (similar to alaboratory beaker) and the screens may include a series of circulardiscs of various sizes. Utilizing the template and screens, a densebottom layer, a middle layer, and a dense top layer may be formed withthe template and screen(s). For example, a dense bottom layer may beformed by applying the reactive and initiated hydrogel precursors to thebase of the template, allowing the reactive precursors to form ahydrogel, and then exposing the hydrogel to an initiator to crosslinkthe initiated precursor(s) thereby forming a dense bottom layer. Amiddle layer may then be formed on top of the bottom layer, by applyingreactive precursors thereto, optionally with initiated precursors, andallowing them to react. A dense top layer may then be formed, forexample, by applying a screen to the middle layer and then applying bothreactive and initiated hydrogel precursors to the middle layer, andallowing the reactive precursors to form a hydrogel layer. The tophydrogel may then be exposed to an initiator to crosslink the initiatedprecursor(s) in the top hydrogel to form a dense top layer. The screenwill prevent crosslinking of any initiated precursors in the middlelayer. The screen may remain or, in embodiments, the screen may beremoved. Thus, the resulting gel will have a denser top layer and adenser bottom layer, and a less dense middle layer.

Each of the layers formed may contain the same or different hydrogelprecursors. Additionally, each of the layers may contain a bioactiveagent. The type and quantity of bioactive agent in each layer may be thesame or different.

A method of forming a two-phase drug delivery hydrogel implant isfurther described with reference to FIG. 3. As shown in FIG. 3, a layerof hydrogel precursors is placed in template 310. The reactiveprecursors form a hydrogel 300 upon exposure to each other. Theinitiated hydrogel precursors are exposed to an initiator 320 toincrease their crosslinking, thereby forming a dense bottom layer. FIG.3B shows several screens 330 of varying sizes. A screen 330 may beplaced on hydrogel 300. Additional precursors may then be added on topof hydrogel 300, allowed to react, and optionally exposed to theinitiator 320 to form the next layer (not shown). This process may berepeated to create a densely crosslinked gel with a core that is lessdense, due to the presence of the screens, which block the exposure ofthe precursors to the initiator. As shown in FIG. 3C, the center 350that was screened may remain less dense than the portion of hydrogel 340not covered by the screens. In embodiments, screens 330 of differentsizes and/shapes may be used to form different centers. The resultingtwo-phase drug delivery hydrogel implant 340 may thus include a moredense hydrogel 340 with a less dense hydrogel 350 forming a centerportion.

Upon placement in situ, the center hydrogel portion 350 of the two-phasedrug delivery hydrogel may degrade at a rate that is faster than that ofthe denser hydrogel 340. The slower degradation rate of the denserhydrogel 340 may thus provide for a gradual release of a bioactive agentover time, with additional release from the less dense center 350 as abolus upon degradation of hydrogel 340. In other embodiments, the centerhydrogel may degrade slower than the surrounding hydrogel allowing for abolus delivery followed by a slow release maintenance dosage. This mayprove beneficial for extended release applications. Immediate/extendedrelease drug delivery systems may be useful for application for examplein delivery of narcotics, anticoagulants, anti-inflammatories,chemotherapeutics, peptides, growth factors, combinations thereof, andthe like.

Another use of a hydrogel according to the present disclosure to form animplant is depicted in FIGS. 5A and 5B. The implant 400 includes a mesh410. The mesh 410 may be coated with an initiator such aspermanganate/acetic acid, ammonium persulfate/acetic acid, potassiumpersulfate/2,2′-azobis[2-(2-dimidazolin-2-yl)propane]dihydrochloride(2,2′-azobis[2-(2-dimidazolin-2-yl)propane]dihydrochloride iscommercially available as VA044 (Wako), ammoniumpersulfate/tetramethylenediamine, combinations thereof, and the like. Amixture of an electrophilic reactive precursor and an initiatedprecursor such as PEG-NHS and PEG-acrylate 420 may be sprayed onto themesh 410. The entire mesh 410 may then be coated with a nucleophilicreactive precursor such as trilysine and additional initiated precursorsuch as unreacted acrylate. The PEG-acrylate contacting the mesh 410 maybe initiated by the permanganate/acetic acid in the mesh and crosslink430. The PEG-NHS and trilysine may also react to form a less denselycross-linked hydrogel 420 across the surface of the entire mesh,including the pores of the mesh 410. As depicted in FIG. 5B, thePEG-NHS-trilysine hydrogel 420 may degrade over a period of time of fromabout 4 days to about 6 days, exposing pores 440 of the mesh 410 therebyallowing space for tissue in-growth. Such a mesh could be used, forexample, in hernia repair.

In other embodiments, as shown in FIG. 6A, the hydrogel of thedisclosure may be utilized to form a suture anchor 600. A syringe 610may inject a mixture 620 of electrophilic and nucleophilic (reactive)hydrogel precursors and an initiated hydrogel precursor beneath tissue630 to form a soft hydrogel 620 both underneath and on the surface 640of the tissue 630. As shown in FIG. 6B, the soft hydrogel 620 may beinitiated with UV light 670 to create a densely cross-linked sutureanchor 650. As shown in FIG. 6C, suture 660 may then be passed throughsuture anchor 650. Such a suture anchor could be used for example, forin situ wound closure, bone anchor, tendon repair, combinations thereof,and the like.

In other embodiments, not shown, one could first initiate the initiatedhydrogel precursor, and then allow the reactive precursors to reactafter formation of the initiated hydrogel.

In yet other embodiments, a rivet may be formed from the hydrogel of thedisclosure to adhere an implant to tissue as shown in FIGS. 7A-C. Animplant 700 may be applied to the peritoneum 710 for hernia correction.A syringe 720 may be used to inject a hydrogel mixture 730 from beneaththe peritoneum 710 (or from above, not shown) through holes 701, 702,703, 704, 705, 706, 707, and 708 of the implant 700. The hydrogelmixture 730 may form a soft hydrogel 740 below the peritoneum, fillingholes 701, 702, 703, 704, 705, 706, 707, and 708, and pooling slightlyon the non-tissue side of the implant 700. The soft hydrogel 740 maythen be exposed to an initiator 750 to form a densely cross-linkedhydrogel rivet 760, thereby adhering the implant 700 to the peritoneum710.

As noted above, in embodiments a hydrogel composition of the presentdisclosure may have varying modulus. One skilled in the art, inembodiments, may tailor the components utilized to form a composition ofthe present disclosure based upon the tissue to which the composition isto be applied. FIG. 10 provides the elastic modulus for various tissues,which may be utilized as a guide in preparing a composition of thepresent disclosure having a desired modulus.

In embodiments, as depicted in FIG. 11, a hydrogel composition may beutilized to fix a defect in tissue. FIG. 11 depicts the use of acomposition of the present disclosure to repair a defect in subchondralbone. The reactive precursors and initiated precursor may be applied toa defect 820 in subchondral bone 865, thereby forming a first hydrogel800 therein. A source of radiation 830 may be applied to the surface ofhydrogel 800 adjacent articular cartilage 855 surrounding the defect,thereby forming a second hydrogel on the surface which functions as abarrier layer 840.

As noted above, in embodiments a hydrogel composition of the presentdisclosure may include one hydrogel dispersed in a second hydrogel. Asdepicted in FIG. 12A, a disperse region 920 may include a core formed ofa second hydrogel formed of an initiated precursor within a firsthydrogel 910 formed of reactive precursors. Alternatively, as depictedin FIG. 12B, many disperse regions 920 may be formed within the firsthydrogel 910. While not depicted in FIGS. 12A and 12B, in someembodiments a barrier layer formed from initiated precursors may beformed over the hydrogel composition of the present disclosure.

A bioactive agent may be included in the first hydrogel, the secondhydrogel, or both. The bioactive agent, in embodiments, may be inliposomes, microspheres, microbubbles, combinations thereof, and thelike. Where a bioactive agent is present in the first and secondhydrogels, the same or difference bioactive agent may be included in thehydrogels. The bioactive agent may be released from the first hydrogelover a period from about 1 day to about 6 weeks, in embodiments fromabout 1 week to about 4 weeks, and the bioactive agent may be releasedfrom the second hydrogel over a period from about 5 days to about 12weeks, in embodiments from about 2 weeks to about 8 weeks.

Examples of compositions including hydrogels with multiple releaseprofiles include those disclosed in U.S. Patent Application PublicationNo. 2009/0047349, the entire disclosure of which is incorporated byreference herein.

The following Examples are being submitted to illustrate embodiments ofthe present disclosure. These Examples are intended to be illustrativeonly and are not intended to limit the scope of the present disclosure.Also, parts and percentages are by weight unless otherwise indicated. Asused herein, “room temperature” refers to a temperature of from about20° C. to about 30° C.

EXAMPLES Example 1 Solution Preparation

First Reactive Precursor: An 80% solution of PEG-diacrylate in phosphatebuffer pH 4.04 was prepared. PEG-NHS was added to this solution at aconcentration of 0.13 g/ml (0.39 grams of PEG-NHS in 3 ml of 80%diacrylate in phosphate buffer).

Second Reactive Precursor: A 0.01 g/ml solution of lysine in boratebuffer was prepared and the pH was adjusted to 8.6.

Initiated Precursor: A 10 mg/ml solution of4,4′-bis(diethyl-amino)benzophenone (excitation wavelength of 365 nm) inethanol was prepared.

Varying amounts of Initiated Precursor solution were added to the FirstReactive Precursor as delineated in Table 2 (below).

Reaction of First and Second Reactive Precursors

Equal volumes of First and Second Reactive Precursors were loaded intoseparate syringes. The syringes were connected and the solutions weremixed for 15 seconds. Next the solutions sat for 15 minutes in order toensure complete crosslinking of the hydrogel.

Crosslinking of Initiated Precursor

Each crosslinked hydrogel was then removed from its respective syringeand cut into several cylinders. The crosslinked hydrogel was thenexposed to varying amounts of UV light (see Table 2) to initiatecrosslinking of the initiated precursor to form an initiated hydrogel.The cylinder of gel was skewered with a long needle, placed under the UVsource, and rotated to allow for even curing.

Hydro gel Composition Testing

Once the cylinders were cured, each was placed under a 12 mm flat probeand compressed to a maximum of 80% of its initial height, or untilbreaking, at a rate of 0.08 mm/sec with a trigger force of 20 grams anda break sensitivity of 5 grams. Results for each cured hydrogel arerecorded in Table 2. FIG. 8 is a bar graph showing the data of Table 2(the sample with 100 microliters of photoinitiator). FIG. 9 is acomparison of the initiated hydrogel (top line) and uninitiated hydrogel(bottom line).

TABLE 2 Microliters of Time (seconds) Max Force in grams InitiatedPrecursor Of UV Exposure % Compression (g) 15 0 80.0 275.60 30 49.1541.70 60 34.8 2607.00 120 42.5 12,187.40 25 0 80.0 221.90 30 78.6827.00 60 40.3 3447.10 120 52.6 16,911.00 25 0 258.80 30 40.6 362.60 6033.2 2140.50 120 52.2 16,304.90 50 0 80.0 308.60 30 67.0 1144.50 60 34.91900.60 120 52.1 14,567.50 100 0 80.0 274.10 30 58.6 378.30 60 35.0772.60 120 33.3 2942.60

Example 2

The preparation of Example 1 was repeated using trilysine in place ofthe lysine in the Second Hydrogel Precursor. Results of the testing areprovided in Table 3 below.

TABLE 3 Microliters of Time (seconds) of Initiated Precursor UV Exposure% Compression Max Force (g) 25 0 79.7 511.00 30 47.5 613.00 60 33.12632.30 120 44.3 11,726.00 50 0 72.9 605.15 60 33.9 1399.40 120 50.115,987.10

As shown by the above Examples, various degrees of crosslinking wereachieved by varying the amount of initiated precursor and the amount ofUV exposure of the initiator. Additionally, depending on the first andsecond hydrogel precursor used, varying levels of crosslinking prior toexposure to UV was achieved.

The above description contains many specifics; these specifics shouldnot be construed as limitations on the scope of the disclosure hereinbut merely as exemplifications of particularly useful embodimentsthereof. Those skilled in the art will envision many other possibilitieswithin the scope and spirit of the disclosure as defined by the claimsappended hereto.

1. A hydrogel composition comprising: a first reactive precursorcomprising a multi-arm polyether possessing electrophilic groups; asecond reactive precursor comprising nucleophilic groups; and at leastone initiated precursor comprising at least one vinyl group.
 2. Thehydrogel composition of claim 1, wherein the first reactive precursor,comprises a core selected from the group consisting of polyethyleneglycol, polyethylene oxide, polyethylene oxide-co-polypropylene oxide,co-polyethylene oxide block copolymers, co-polyethylene oxide randomcopolymers, and combinations thereof, and wherein the second reactiveprecursor comprises a core comprising a component selected from thegroup consisting of polyethylene glycol, polyethylene oxide,polyethylene oxide-co-polypropylene oxide, co-polyethylene oxide blockcopolymers, co-polyethylene oxide random copolymers, polyvinyl alcohol,poly(vinyl pyrrolidinone), poly(amino acids), dextran, chitosan,alginates, carboxymethylcellulose, oxidized cellulose,hydroxyethylcellulose, hydroxymethylcellulose, hyaluronic acid, albumin,collagen, casein, gelatin, and combinations thereof.
 3. The hydrogelcomposition of claim 1, wherein the first reactive precursor possessesN-hydroxysuccinimide groups and the second reactive precursor possessesamine groups.
 4. The hydrogel composition of claim 1, wherein theinitiated precursor is selected from the group consisting of acrylicacid, methacrylic acid, phosphorylcholine containing monomers, furanonefunctional vinyl monomers, potassium sulfopropyl acrylate, potassiumsulfopropyl methacrylate, n-vinyl pyrrolidone, hydroxyethylmethacrylate, vinyl monomers having a high refractive index, siloxanefunctional vinyl compounds, polyethylene glycol-silicone co-monomershaving vinyl groups, tris acrylate, pyrrole, liquid crystalline vinylmonomers, liquid crystalline vinyl polymers, and combinations thereof.5. The hydrogel composition of claim 1, further comprising an initiatorselected from the group consisting of redox initiators, free radicalinitiators, radiation, and combinations thereof.
 6. The hydrogelcomposition of claim 5, wherein the radiation is selected from the groupconsisting of heat, visible light, ultraviolet light, gamma ray, andelectron beam.
 7. The hydrogel composition of claim 1, furthercomprising a bioactive agent.
 8. The hydrogel composition of claim 1,wherein the initiated precursor comprises from about 5% to about 30% byweight of the hydrogel composition.
 9. The hydrogel composition of claim1, wherein the first reactive precursor reacts with the second reactiveprecursor to form a first hydrogel, and the initiated precursor forms asecond hydrogel upon exposure with the initiator.
 10. The hydrogelcomposition of claim 8, wherein the first hydrogel has a modulus of fromabout 5 kPa to about 90 kPa, and the second hydrogel has a modulus offrom about 50 kPa to about 5,000 kPa.
 11. The hydrogel composition ofclaim 8, wherein the first hydrogel degrades over a period of from about1 week to about 12 weeks, and the second hydrogel degrades over a periodof at least about 2 weeks.
 12. A method comprising: contacting a firstreactive precursor with a second reactive precursor and an initiatedprecursor comprising at least one vinyl group; crosslinking the firstreactive precursor and the second reactive precursor to form a firsthydrogel; and exposing the initiated precursor to an initiator toinitiate crosslinking of the initiated precursor.
 13. The method ofclaim 12, wherein the first reactive precursor comprises electrophilicgroups and the second reactive precursor comprises nucleophilic groups.14. The method of claim 12, wherein the first reactive precursor, thesecond reactive precursor, or both, comprise a core comprising acomponent selected from the group consisting of polyethylene glycol,polyethylene oxide, polyethylene oxide-co-polypropylene oxide,co-polyethylene oxide block copolymers, co-polyethylene oxide randomcopolymers, polyvinyl alcohol, poly(vinyl pyrrolidinone), poly(aminoacids), dextran, chitosan, alginates, carboxymethylcellulose, oxidizedcellulose, hydroxyethylcellulose, hydroxymethylcellulose, hyaluronicacid, albumin, collagen, casein, gelatin, and combinations thereof. 15.The method of claim 12, wherein the first reactive precursor possessesN-hydroxysuccinimide groups and the second reactive precursor possessesamine groups.
 16. The method of claim 12, wherein the initiatedprecursor is selected from the group consisting of acrylic acid,methacrylic acid, phosphorylcholine containing monomers, furanonefunctional vinyl monomers, potassium sulfopropyl acrylate, potassiumsulfopropyl methacrylate, n-vinyl pyrrolidone, hydroxyethylmethacrylate, vinyl monomers having a high refractive index, siloxanefunctional vinyl compounds, polyethylene glycol-silicone co-monomershaving vinyl groups, tris acrylate, pyrrole, liquid crystalline vinylmonomers, liquid crystalline vinyl polymers, and combinations thereof.17. The method of claim 12, further comprising an initiator selectedfrom the group consisting of redox initiators, free radical initiators,radiation, and combinations thereof.
 18. The method of claim 17, whereinthe radiation is selected from the group consisting of heat, visiblelight, ultraviolet light, gamma ray, and electron beam.
 19. The methodof claim 12, wherein the hydrogel further comprises a bioactive agent.20. The method of claim 19, wherein crosslinking the initiated precursorforms a barrier layer on an external surface of the first hydrogel,thereby directing delivery of the bioactive agent from the firsthydrogel in a direction opposite the barrier layer.
 21. The method ofclaim 12, wherein the first reactive precursor and second reactiveprecursor are applied to a defect in tissue, and wherein crosslinkingthe initiated precursor forms a barrier layer on a surface of the firsthydrogel covering the defect in tissue.
 22. The method of claim 21,wherein the first hydrogel has a modulus of from about 5 kPa to about 90kPa, and the barrier layer has a modulus of from about 50 kPa to about5,000 kPa.
 23. The method of claim 21, wherein the first hydrogeldegrades over a period of from about 1 week to about 12 weeks, and thebarrier layer degrades over a period of at least about 2 weeks.
 24. Themethod of claim 12, wherein the first reactive precursor, the secondreactive precursor, and the initiated precursor are contacted with eachother and form the first hydrogel in situ.
 25. The method of claim 12,wherein the first hydrogel is utilized as a component selected from thegroup consisting of adhesives, hemostats, sealants, implants, protectivebarriers, drug delivery devices, and combinations thereof.
 26. Themethod of claim 12, wherein the first reactive precursor, the secondreactive precursor, and the initiated precursor are contacted with eachother and form the first hydrogel ex vivo.
 27. The method of claim 25,wherein the precursors are applied to a template prior to formation ofthe first hydrogel.
 28. The method of claim 12, wherein crosslinking theinitiated precursor forms a second hydrogel having a differing modulusthan the first hydrogel.
 29. The method of claim 28, wherein the firsthydrogel and the second hydrogel form an interpenetrating network. 30.The method of claim 29, wherein the first hydrogel degrades more quicklythan the second hydrogel, thereby forming spaces permitting healingcomprising tissue in-growth, vascularization, and combinations thereof.